Jane version(s) affected: 7.9.0

Description
I expect that when using oneOf to make an object property nullable, that the NotNullValidator is not used for that property.

How to reproduce

Using a schema with a property like this, enable validation for Jane, and generate the classes. The MyObjectConstraint class will have a NotNullValidator for the myProperty property.

// myObject.json
{
    "type": "object",
    "properties": {
        "myProperty": {
            "oneOf": [
                {
                    "type": "null"
                },
                {
                    "$ref": "/ref/to/myPropertySchema.json"
                }
            ]
        }
    },
    "required": [
    ],
    "additionalProperties": false,
}

Possible Solution

In the ObjectGuesser class, you already check if the property is nullable by checking the 'type' property of each of the oneOf values:

        "myProperty": {
            "oneOf": [
                {
                    "type": "null" <=== this one
                },
                {
                    "$ref": "/ref/to/myPropertySchema.json" <==== and the one inside here
                }
            ]
        }

That works correctly. Once the data is passed to the ChainValidator's guess method, that is ignored.

The NotNullValidator checks the 'type' property of the object that contains the oneOf values:

        "myProperty": {
            "oneOf": [
                {
                    "type": "null"
                },
                {
                    "$ref": "/ref/to/myPropertySchema.json"
                }
            ]
            // type <==== this one, which is null because I never set one
        }

To fix this, I think you can do one of the following:

• update the NotNullValidator's guess method to include handling for oneOf for JsonSchema
• update the ChainValidator to check the nullable property of the Property $guess parameter it to skip the NotNullValidator
• have the NotNullValidator check the nullable property by passing the $guess to it

Additional context